Joan Plowright missing from final scene -- ideas?

Unlikely anyone will have an answer to this, but on the off chance....

At the end of the movie, the three Cissies get out of the boat into the water and, briefly, we see the youngest swimming alone among the red flowers, then the middle Cissie, same deal, but even though we see Joan Plowright removing some of her clothing and from all appearances about to get out of the boat, we never see her swimming.

It's probably a pedestrian reason: maybe because she was older and it was cold or she didn't want to/couldn't swim in water that deep.

I read somewhere that the weather was terrible when Juliet Stevenson swims in the sea to drown her husband and ended up miserably sick. In any case, if anyone knows....